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</div><div></div></div></div></div><div class="t-navbar-sep"> </div></div>
<p>终止当前函数并返回指定值（若存在）给调用方函数。
</p>
<h3><span class="mw-headline" id=".E8.AF.AD.E6.B3.95">语法</span></h3>
<table class="t-sdsc-begin">

<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">属性</span><span class="t-mark">(可选)</span> <code><b>return</b></code> <span class="t-spar">表达式</span><span class="t-mark">(可选)</span> <code><b>;</b></code>
</td>
<td> (1)
</td>
<td class="t-sdsc-nopad">
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">属性</span><span class="t-mark">(可选)</span> <code><b>return</b></code> <span class="t-spar">花括号初始化器列表</span> <code><b>;</b></code>
</td>
<td> (2)
</td>
<td> <span class="t-mark-rev t-since-cxx11">(C++11 起)</span>
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">属性</span><span class="t-mark">(可选)</span> <code><b>co_return</b></code> <span class="t-spar">表达式</span><span class="t-mark">(可选)</span> <code><b>;</b></code>
</td>
<td> (3)
</td>
<td> <span class="t-mark-rev t-since-cxx20">(C++20 起)</span>
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr>
<tr class="t-sdsc">
<td> <span class="t-spar">属性</span><span class="t-mark">(可选)</span> <code><b>co_return</b></code> <span class="t-spar">花括号初始化器列表</span> <code><b>;</b></code>
</td>
<td> (4)
</td>
<td> <span class="t-mark-rev t-since-cxx20">(C++20 起)</span>
</td></tr>



<tr>
<td colspan="10" class="t-sdsc-sep">
</td></tr></table>
<table class="t-par-begin">


<tr class="t-par">
<td>  <span class="t-spar">属性</span><span class="t-mark-rev t-since-cxx11">(C++11)</span>
</td>
<td> -
</td>
<td>  任意数量<a href="attributes.html" title="cpp/language/attributes">属性</a>
</td></tr>
<tr class="t-par">
<td>  <span class="t-spar">表达式</span>
</td>
<td> -
</td>
<td>  可转换到函数返回类型的<a href="expressions.html" title="cpp/language/expressions">表达式</a>
</td></tr>
<tr class="t-par">
<td>  <span class="t-spar">花括号初始化器列表</span>
</td>
<td> -
</td>
<td>  初始化器的花括号环绕列表，及其他花括号初始化器列表
</td></tr></table>
<h3><span class="mw-headline" id=".E8.A7.A3.E9.87.8A">解释</span></h3>
<div class="t-li1"><span class="t-li">1)</span> 对 <span class="t-spar">表达式</span> 求值，终止当前函数，并将 <span class="t-spar">表达式</span> <a href="implicit_cast.html" title="cpp/language/implicit conversion">隐式转换</a>到函数返回类型后的结果返回给调用方。<span class="t-spar">表达式</span> 在返回类型为（可有 cv 限定的）<span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span> 的函数中、构造函数中和析构函数中可选。</div>
<div class="t-li1"><span class="t-li">2)</span> 使用<a href="list_initialization.html" title="cpp/language/list initialization">复制列表初始化</a>对函数的返回值进行构造。</div>
<div class="t-li1"><span class="t-li">3,4)</span> 在协程中，对于最终暂停点，必须用关键字 <code>co_return</code> 取代 <code>return</code>（细节见<a href="coroutines.html" title="cpp/language/coroutines">协程</a>）。</div>
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">注解</span></h3>
<p>若控制流抵达返回 <code>void</code>（可有 cv 限定）的函数结尾，构造函数结尾，析构函数结尾，或返回 <code>void</code>（可有 cv 限定）的函数的<a href="function-try-block.html" title="cpp/language/function-try-block">函数 try 块</a>结尾，则执行 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span><span class="sy4">;</span></span></span>。
</p><p>若控制流抵达 <a href="main_function.html" title="cpp/language/main function">main 函数</a>的结尾，则执行 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw1">return</span> <span class="nu0">0</span><span class="sy4">;</span></span></span>。
</p><p>控制流出有返回值的函数（除了 <span class="t-c"><span class="mw-geshi cpp source-cpp">main</span></span>）的结尾而不经过 return 语句是未定义行为。
</p><p>在返回 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span> 的函数中，当表达式类型为 <span class="t-c"><span class="mw-geshi cpp source-cpp"><span class="kw4">void</span></span></span> 时，可以使用带 <span class="t-spar">表达式</span> 的 return 语句。
</p>
 <table class="t-rev-begin">
<tr class="t-rev t-since-cxx14"><td>
<p>对函数调用结果的复制初始化<a href="eval_order.html" title="cpp/language/eval order">按顺序早于</a>在 <span class="t-spar">表达式</span> 结尾处对所有临时量的销毁，后者<i>按顺序早于</i>该 return 的外围块的局部变量的销毁。
</p>
</td>
<td><span class="t-mark-rev t-since-cxx14">(C++14 起)</span></td></tr>
</table>
<p>以值返回可能会涉及临时对象的构造和复制/移动，除非使用<a href="copy_elision.html" title="cpp/language/copy elision">复制消除</a>。具体而言，复制/移动的条件如下：
</p>
 <table class="t-rev-begin">
<tr class="t-rev t-since-cxx11"><td>
<h4> <span class="mw-headline" id=".E8.87.AA.E5.8A.A8.E4.BB.8E.E5.B1.80.E9.83.A8.E5.8F.98.E9.87.8F.E5.92.8C.E5.BD.A2.E5.8F.82.E7.A7.BB.E5.8A.A8">自动从局部变量和形参移动</span></h4>
<p>若 <span class="t-spar">表达式</span> 是（可有括号的）<a href="name.html" title="cpp/language/identifiers">标识表达式</a>并且指名类型如下的变量：
</p>
<dl><dd><ul><li> 非 volatile 对象类型
</li></ul>
</dd></dl>
 <table class="t-rev-begin">
<tr class="t-rev t-since-cxx20"><td>
<dl><dd><ul><li> 或到对象类型的非 volatile 右值引用类型
</li></ul>
</dd></dl>
</td>
<td><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></td></tr>
</table>
<p>，而该变量声明于
</p>
<dl><dd> 最内层外围函数或 lambda 表达式
<ul><li> 的体内，或
</li><li> 为其形参
</li></ul>
</dd></dl>
<p>则进行<i>两次</i><a href="overload_resolution.html" title="cpp/language/overload resolution">重载决议</a>，以选择用于初始化返回值的构造函数<span class="t-rev-inl t-since-cxx20"><span>，或对于 <span class="t-c"><span class="mw-geshi cpp source-cpp">co_return</span></span> 为选择 <span class="t-c"><span class="mw-geshi cpp source-cpp">promise.<span class="me1">return_value</span><span class="br0">(</span><span class="br0">)</span></span></span> 的重载</span> <span><span class="t-mark-rev t-since-cxx20">(C++20 起)</span></span></span>：
</p>
<ul><li> 首先如同假设 <span class="t-spar">表达式</span> 是右值表达式（从而它可选择<a href="move_constructor.html" title="cpp/language/move constructor">移动构造函数</a>），然后
</li></ul>
<dl><dd><ul><li> 若第一次重载决议失败
</li></ul>
</dd></dl>
 <table class="t-rev-begin">
<tr class="t-rev t-until-cxx20"><td>
<dl><dd><ul><li> 或若它成功，但不选择<a href="move_constructor.html" title="cpp/language/move constructor">移动构造函数</a>（正式而言，选择的构造函数的首参数不是到 <span class="t-spar">表达式</span> 类型的（可有 cv 限定）的右值引用，
</li></ul>
</dd></dl>
</td>
<td><span class="t-mark-rev t-until-cxx20">(C++20 前)</span></td></tr>
</table>
<ul><li> 则照常进行重载决议，把 <span class="t-spar">表达式</span> 当做左值（故它可以选择<a href="copy_constructor.html" title="cpp/language/copy constructor">复制构造函数</a>）。
</li></ul>
</td>
<td><span class="t-mark-rev t-since-cxx11">(C++11 起)</span></td></tr>
</table>
 <table class="t-rev-begin">
<tr class="t-rev t-since-cxx17"><td>
<h4> <span class="mw-headline" id=".E5.8F.97.E4.BF.9D.E8.AF.81.E7.9A.84.E5.A4.8D.E5.88.B6.E6.B6.88.E9.99.A4"> 受保证的复制消除 </span></h4>
<p>若 <span class="t-spar">表达式</span> 是纯右值，则直接以该表达式初始化结果对象。当其类型相匹配时，这之中并不涉及复制或移动构造函数（见<a href="copy_elision.html" title="cpp/language/copy elision">复制消除</a>）。
</p>
</td>
<td><span class="t-mark-rev t-since-cxx17">(C++17 起)</span></td></tr>
</table>
<h3><span class="mw-headline" id=".E5.85.B3.E9.94.AE.E8.AF.8D">关键词</span></h3>
<p><a href="../keyword/return.html" title="cpp/keyword/return"><tt>return</tt></a>,
<a href="../keyword/co_return.html" title="cpp/keyword/co return"><tt>co_return</tt></a>
</p>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">示例</span></h3>
<div class="t-example"><div class="t-example-live-link"><div class="coliru-btn coliru-btn-run-init">运行此代码</div></div>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="cpp source-cpp"><pre class="de1"><span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;string&gt;</span>
<span class="co2">#include &lt;utility&gt;</span>
 
<span class="kw4">void</span> fa<span class="br0">(</span><span class="kw4">int</span> i<span class="br0">)</span>
<span class="br0">{</span>
    <span class="kw1">if</span> <span class="br0">(</span>i <span class="sy1">==</span> <span class="nu0">2</span><span class="br0">)</span>
         <span class="kw1">return</span><span class="sy4">;</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> i <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
<span class="br0">}</span> <span class="co1">// 隐含的 return;</span>
 
<span class="kw4">int</span> fb<span class="br0">(</span><span class="kw4">int</span> i<span class="br0">)</span>
<span class="br0">{</span>
    <span class="kw1">if</span> <span class="br0">(</span>i <span class="sy1">&gt;</span> <span class="nu0">4</span><span class="br0">)</span>
         <span class="kw1">return</span> <span class="nu0">4</span><span class="sy4">;</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> i <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
    <span class="kw1">return</span> <span class="nu0">2</span><span class="sy4">;</span>
<span class="br0">}</span>
 
<a href="../utility/pair.html"><span class="kw1096">std::<span class="me2">pair</span></span></a><span class="sy1">&lt;</span><a href="../string/basic_string.html"><span class="kw1230">std::<span class="me2">string</span></span></a>, <span class="kw4">int</span><span class="sy1">&gt;</span> fc<span class="br0">(</span><span class="kw4">const</span> <span class="kw4">char</span><span class="sy2">*</span> p, <span class="kw4">int</span> x<span class="br0">)</span>
<span class="br0">{</span>
    <span class="kw1">return</span> <span class="br0">{</span>p, x<span class="br0">}</span><span class="sy4">;</span>
<span class="br0">}</span>
 
<span class="kw4">void</span> fd<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    <span class="kw1">return</span> fa<span class="br0">(</span><span class="nu0">10</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// fa(10) 是 void 表达式</span>
<span class="br0">}</span>
 
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
    fa<span class="br0">(</span><span class="nu0">2</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 返回，当 i==2 时无动作</span>
    fa<span class="br0">(</span><span class="nu0">1</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 打印其实参，然后返回</span>
    <span class="kw4">int</span> i <span class="sy1">=</span> fb<span class="br0">(</span><span class="nu0">5</span><span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 返回 4</span>
    i <span class="sy1">=</span> fb<span class="br0">(</span>i<span class="br0">)</span><span class="sy4">;</span> <span class="co1">// 打印其实参，返回 2</span>
    <a href="../io/cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> i <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span>
              <span class="sy1">&lt;&lt;</span> fc<span class="br0">(</span><span class="st0">"Hello"</span>, <span class="nu0">7</span><span class="br0">)</span>.<span class="me1">second</span> <span class="sy1">&lt;&lt;</span> <span class="st0">'<span class="es1">\n</span>'</span><span class="sy4">;</span>
    fd<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div></div>
<p>输出：
</p>
<div dir="ltr" class="mw-geshi" style="text-align: left;"><div class="text source-text"><pre class="de1">1
4
2
7
10</pre></div></div> 
</div>
<h3><span class="mw-headline" id=".E7.BC.BA.E9.99.B7.E6.8A.A5.E5.91.8A">缺陷报告</span></h3>
<p>下列更改行为的缺陷报告追溯地应用于以前出版的 C++ 标准。
</p>
<table class="dsctable" style="font-size:0.8em">
<tr>
<th> DR
</th>
<th> 应用于
</th>
<th> 出版时的行为
</th>
<th> 正确行为
</th></tr>
<tr>
<td> <a rel="nofollow" class="external text" href="https://wg21.cmeerw.net/cwg/issue1579">CWG 1579</a>
</td>
<td> C++11
</td>
<td> 不允许经由转换移动构造函数返回
</td>
<td> 启用对转换移动构造函数的查找
</td></tr>
<tr>
<td> <a rel="nofollow" class="external text" href="https://wg21.cmeerw.net/cwg/issue1885">CWG 1885</a>
</td>
<td> C++14
</td>
<td> 自动变量的销毁顺序不明确
</td>
<td> 添加了定序规则
</td></tr></table>
<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">参阅</span></h3>
<table class="t-dsc-begin">

</table>

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